/*
 * Copyright 2002-2019 Intel Corporation.
 * 
 * This software is provided to you as Sample Source Code as defined in the accompanying
 * End User License Agreement for the Intel(R) Software Development Products ("Agreement")
 * section 1.L.
 * 
 * This software and the related documents are provided as is, with no express or implied
 * warranties, other than those that are expressly stated in the License.
 */


#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>
#include <syscall.h>
#include <linux/unistd.h>
#include <asm/ldt.h>
#include <errno.h>
#include <string.h>
#include <sys/utsname.h>

#ifndef __NR_set_thread_area
#   define __NR_set_thread_area 243
#endif
#ifndef __NR_get_thread_area
#   define __NR_get_thread_area 244
#endif
#ifndef SYS_set_thread_area
#   define SYS_set_thread_area __NR_set_thread_area
#endif
#ifndef SYS_get_thread_area
#   define SYS_get_thread_area __NR_get_thread_area
#endif


typedef struct {
    unsigned int  entry_number;
    unsigned int  base_addr;
    unsigned int  limit;
    unsigned int  seg_32bit:1;
    unsigned int  contents:2;
    unsigned int  read_exec_only:1;
    unsigned int  limit_in_pages:1;
    unsigned int  seg_not_present:1;
    unsigned int  useable:1;
}UserDesc;

# define TLS_GET_GS_REG() \
  ({ int __seg; __asm ("movw %%gs, %w0" : "=q" (__seg)); __seg & 0xffff; })

#  define TLS_SET_GS_REG(val) \
  __asm ("movw %w0, %%gs" :: "q" (val))

# define TLS_GET_FS_REG() \
  ({ int __seg; __asm ("movw %%fs, %w0" : "=q" (__seg)); __seg & 0xffff; })

#  define TLS_SET_FS_REG(val) \
  __asm ("movw %w0, %%fs" :: "q" (val))

typedef struct
{
    unsigned int d1;
    unsigned int d2;
}UserInfo;

#define GDT_NUM_OF_ENTRIES   3
#define GDT_ENTRIES 16


unsigned int GdtFirstEntry()
{
    static int first = 0;
    if (first) return first;

    UserDesc thrDescr;

    for (int i=0; i< GDT_ENTRIES; i++)
    {
        thrDescr.entry_number = i;
        int res = syscall(SYS_get_thread_area, &thrDescr);
        if ((res == 0) || (errno != EINVAL))
        {
            first = i;
            return first;
        }
    }
    fprintf(stderr, "First GDT entry is not found\n");
    exit(-1);
}

int main (int argc, char *argv[])
{
    int rc;
    int i;
    UserDesc tr;
    UserDesc set_tr;
    int res;

    tr.entry_number = GdtFirstEntry();
    res = syscall(SYS_get_thread_area, &tr);
    if (res != 0)
    {
        printf("SYS_get_thread_area failed with error: %s\n", strerror(errno));
        return 0;
    }

    tr.entry_number = (unsigned)-1;
    tr.base_addr = 0xabcd;

    res = syscall(SYS_set_thread_area, &tr);
    if (res != 0)
    {
        printf("SYS_set_thread_area failed with error: %s\n", strerror(errno));
        return 0;
    }

    printf("Allocated entry is %d\n", tr.entry_number);


    memset(&set_tr, 0, sizeof(UserDesc));
    set_tr.entry_number = tr.entry_number;
    set_tr.read_exec_only = 1;
    set_tr.seg_not_present = 1;
    set_tr.useable = 0;

    printf("Free entry %d\n", set_tr.entry_number);
    res = syscall(SYS_set_thread_area, &set_tr);
    if (res != 0)
    {
        printf("SYS_set_thread_area failed with error: %s\n", strerror(errno));
        return 0;
    }


    tr.entry_number = (unsigned)-1;
    tr.base_addr = 0xcdef;
    res = syscall(SYS_set_thread_area, &tr);
    if (res != 0)
    {
        printf("SYS_set_thread_area failed with error: %s\n", strerror(errno));
        return 0;
    }
    printf("Allocated entry is %d\n", tr.entry_number);

    tr.base_addr = 0;
    res = syscall(SYS_get_thread_area, &tr);
    if (res != 0)
    {
        printf("SYS_get_thread_area failed with error: %s\n", strerror(errno));
        return 0;
    }
    printf("Base address for entry %d is 0x%x\n", tr.entry_number, tr.base_addr);

    tr.entry_number = GdtFirstEntry()+2;
    res = syscall(SYS_get_thread_area, &tr);
    if (res != 0)
    {
        printf("SYS_get_thread_area failed with error: %s\n", strerror(errno));
        return 0;
    }
    printf("Base address for entry %d is 0x%x\n", tr.entry_number, tr.base_addr);

    return 0;
}

